New Kenyan Fossils Expand The Range Of Australopithecus

Comparative photographs of fossil hominin ulnae. KNM-RK 53525 was discovered at the Kantis Fossil Site. Scale bar = 1 cm. E. Mbua et al., Journal of Human Evolution 2016
Janet Fang 24/03/2016, 22:28

Researchers studying fossils uncovered in the outskirts of Nairobi reveal that they belonged to the same species as Lucy, Australopithecus afarensis. This is the first time a fossil from this extinct genus was discovered east of the Rift Valley, suggesting that the range of our Australopithecus ancestors was much bigger than we thought. The findings are published in the May issue of Journal of Human Evolution

A. afarensis is known from East African sites dating back between 3.7 and 3 million years. They lived in a wide spectrum of habitats from northern Ethiopia to northern Tanzania, including woodlands at Laetoli, mixed woodland and shrubland at Hadar, and floodplain grassland at Maka. Now, according to a team led by Mount Kenya University’s Emma Mbua and Masato Nakatsukasa of Kyoto University, A. afarensis also lived much farther east in the highlands of Kenya – at what they’ve now named the Kantis Fossil Site. 

Located on the eastern shoulder of the Gregory Rift Valley, the Kantis bone bed was noted during a geological survey in 1991. However, no research had been conducted until 2009, when the owner of a farm next to the small, seasonal Kantis river reported the site to researchers. The farm owner’s family had seen fossilized bones on the dry Kantis valley back in the 1970s. 

In the last few years, the team has collected 1,200 fossil elements from the Kantis Fossil Site belonging to 28 animal groups and one human ancestor. They’ve identified a few A. afarensis teeth and one forearm representing two juveniles and an adult. Based on the size and development of muscle attachment marks, the left ulna (KNM-RK 53525, pictured above) likely came from an adult male. "This has important implications for what we understand about our ancestor's distribution range," Nakatsukasa says in a statement, "namely that Australopithecus could have covered a much greater area by this age."

The team also identified the remains of fossil hippos, rhinos, horses, giraffes, elephants, and cats. The composition of the Kantis fauna, combined with stable carbon isotopic data, suggest that this site 3.5 million years ago was like that of other A. afarensis sites on the Rift Valley floor, but more open. It was mostly grassland with a perennial body of water and few trees.

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